Pretty fun and addicting.
I have a question though: The permanent upgrade achievement isn't showing up. Should I just try the whole game without upgrades? I'm trying to do that now but I'm now stuck fighting Jesus.
EDIT: And apparently "permanent upgrades" meant no upgrades from the map's upgrade menu. Wow that was difficult!
A survival mode or something would be fun as well. Or maybe adding so that we're the ones attacking whilst the enemy defend?